Two of us are going to Rome in the latter half of June. We were thinking about taking two or three days to see some other sites in Italy. We thought that it might be possible to see Assisi (for which I understand a full day is not really needed -- I've heard that it is a very commercialized place; other than the Basilica and St. Clare, etc., there's not much else worth seeing, correct me if I am wrong), Orvieto, and then either Siena or Florence.
(We know that we're not going to get to see everything in such a short time)
What I am hoping to determine is: is it even remotely reasonable to consider visiting these three cities in three days -- i.e. only hitting the main sites --, and if so, is it possible to do it via public transportation (train or bus)? We thought about leaving on a Thursday or Friday and coming back Sunday. AutoEurope charges about $200 for their cheapest rental car for three days, which looks approximately like a washing machine on wheels. I've had a really hard time figuring out bus or train fares online and what would be the best route to take. We are traveling on something of a shoestring and so hope to keep costs as low as possible (will probably stay in convents, etc.) while not at the same time making the travel extremely tedious.
I would appreciate any advice on this matter. The main part of our trip will be visiting Rome, but we did hope to take about three days out of our 13 days total to see some of the other nearby towns of religious and cultural interest, probably Orvieto, Assisi, and Florence or Siena.
Many thanks.